Anatomic Locations of Aortic Dissection
Aortic dissection can occur anywhere along the entire length of the aorta—from the aortic root through the ascending aorta, aortic arch, descending thoracic aorta, and into the abdominal aorta—though certain segments are more vulnerable than others. 1
Primary Anatomic Segments
The thoracic aorta is divided into four distinct segments where dissection can originate or propagate 1:
- Aortic root: Includes the aortic valve annulus, valve cusps, and sinuses of Valsalva 1
- Ascending aorta: Extends from the sinotubular junction to the brachiocephalic artery origin 1
- Aortic arch: Begins at the brachiocephalic artery origin and includes the origins of head and neck vessels 1
- Descending thoracic aorta: Begins at the isthmus between the left subclavian artery and ligamentum arteriosum, courses anterior to the vertebral column, and continues through the diaphragm 1
Most Common Sites of Dissection Origin
The proximal descending thoracic aorta (just distal to the left subclavian artery) is the most prone location for both early and late dissection. 2 This represents the classic origin point for Stanford Type B dissections 1.
The ascending aorta is the second most common site, particularly in patients with genetic conditions like Marfan syndrome or bicuspid aortic valve 2. Type A dissections involving the ascending aorta are more immediately life-threatening due to risk of pericardial tamponade, aortic valve regurgitation, and coronary ostial involvement 1, 3.
Dissection Propagation Patterns
Dissection does not remain localized—it propagates along the aortic wall in characteristic patterns 1:
- Antegrade dissection: The intimal tear is proximal to the distal end of dissection, with blood tracking distally 1
- Retrograde dissection: The tear is located distal to the proximal end, with blood tracking proximally toward the heart 1, 4
- Bidirectional extension: Dissection can propagate both directions from the entry tear 1
Up to 20% of Type B dissections originating at the aortic isthmus can extend retrograde into the ascending aorta, converting to Type A dissection. 1 This retrograde extension is particularly dangerous as it transforms a medically managed condition into a surgical emergency 4.
Abdominal Aortic Involvement
While less common as an origin site, the infrarenal abdominal aorta can be involved through distal propagation of thoracic dissections 1, 2. The DeBakey Type IIIb classification specifically describes dissections extending below the diaphragm into the abdominal aorta 1.
Branch Vessel Involvement
Dissection can extend into any aortic branch vessel, occurring in up to one-third of patients. 5 This includes:
- Coronary arteries (causing acute myocardial infarction) 3
- Brachiocephalic and carotid arteries (causing stroke) 1
- Renal arteries (causing renal malperfusion) 1
- Mesenteric arteries (causing bowel ischemia) 5
Clinical Pitfall
More than half of patients presenting with dissection have aortic diameters less than 5.5 cm, and dissection can occur even with normal aortic diameter. 6 This means you cannot exclude dissection based on aortic size alone—the location and hemodynamic stress patterns matter more than absolute diameter in many cases 1.
The aortic isthmus (between left subclavian artery and ligamentum arteriosum) is the site of greatest mechanical stress, explaining why 95% of traumatic aortic injuries occur at this location 6. This same biomechanical vulnerability makes it a common site for spontaneous dissection 1.